1. Field of the Invention
The present invention relates to a sheet feeding device which separates and conveys stacked recording media one by one, and a recording apparatus on which the sheet feeding device is mounted.
2. Description of the Related Art
A recording apparatus such as a printer, a photocopying machine or a facsimile machine includes a sheet feeding device which stacks and contains a plurality of recording media in a sheet feeding tray, and separates and feeds the stacked and contained recording media one by one. As separation systems for the recording media in the sheet feeding device, many constitutions have been suggested, and as one of the constitutions, an inclined surface separation system is known where a front edge of each recording medium is made to abut on a separating member disposed on an inclined surface which is inclined to a traveling direction of the recording media, thereby separating the recording media. The sheet feeding device of the inclined surface separation system is disclosed in JP-A-2008-239272 and JP-A-2004-075394.
JP-A-2008-239272 discloses a sheet feeding device where a plurality of separation claw pieces are fixedly arranged along an inclined surface on which the recording media abut. In this sheet feeding device, to prevent the double-sheets feeding of the recording media, the separation claw pieces are formed so that an angle of each claw piece to the inclined surface on a downstream side (a vertex side of the inclined surface) in a traveling direction becomes smaller than on an upstream side (a foot side of the inclined surface) in the traveling direction.
Moreover, JP-A-2004-075394 discloses a sheet feeding device where a separating member having projections formed along an inclined surface is disposed. This separating member is movable along the inclined surface, a base end of the separating member on a bottom side of a sheet feeding tray is formed in a cantilever-like constitution, or the separating member turns around a portion of the separating member which is a turn center, so that a further improved separation performance is exerted, when each recording medium abuts on the inclined surface.
In a recording apparatus, there are used various types of recording media having different characteristics, for example, recording media called plain papers and having a low rigidity, recording media called photograph sheets and having a high rigidity, and the like. For example, since the plain papers have the low rigidity, it is difficult to separate the papers one by one, but since the photograph sheets have the high rigidity, the sheets can easily be separated one by one.
It is not easy to separate the recording media having the different characteristics one by one in this way by use of a common sheet feeding device of an inclined surface separation system. That is, a resistance required to separate the recording media in the inclined surface separation system (a relative relation between the required resistance and a limited resistance) varies for each type of the recording media. Therefore, it is not possible to set such a relation between the resistances as to enable the suitable separation of any recording media.
For example, in the separation device disclosed in JP-A-2004-075394, the separating member is movable. In the constitution where the member moves along the inclined surface, however, it is not possible to create such a difference of the frictions as to assure the separating operations of the recording media having the different characteristics. Moreover, in the constitution where the separating member turns around a portion of the member which is a supporting point, the resistances are different between an inclined state of the separating member in a case where an amount of the stacked recording media is small and an inclined state of the separating member in a case where the amount is large. In consequence, the relation between the resistances changes in accordance with a stack position, and even when the same type of recording media are separated, the media cannot suitably be separated.
Moreover, when the photograph sheets are used as the recording media, there is a possibility that an excessively large resistance is applied to a front edge of each photograph sheet that comes in contact with the separating member to peel off the coating surface of the photograph sheet, if the separating resistance is not suitably set. Furthermore, there is known a constitution where a U-turn-like path is employed as a conveyance path of the recording media for the purpose of making the recording apparatus smaller. For example, when the photograph sheets are used in this recording apparatus, the separating member abuts on a recording surface (the coating surface), and hence there is also a possibility that the coating surface is damaged, when an unsuitable resistance is applied.